cmux-next agent pane: keep the session picker, history and lag recovery in sync with the daemon

[teamleaderleo]

Summary

These are the four client-side fixes from #16203 that the React agent pane (#16231) didn't include, ported to webviews/src/agent-session/acpmux/direct.ts:

• Session picker: it refreshes on every session-list change. Before, a session created, updated or purged elsewhere left the picker stale.
• Older history: it now pages through _acpmux/events instead of reattaching, and stops when the daemon replies more: false. Reattaching replaced the live summary and queue and dropped a pending permission. A page that lands after the selection changed is discarded.
• Closed socket: a request on a socket that isn't open rejects at once instead of hanging.
• _acpmux/lagged: it fetches the missed events and merges them, instead of being ignored. It follows the daemon's real notice shapes: {sessionIds, watch, dropped} from agent-gui daemons and {dropped} from older ones, where no sessionIds means the selected session. It pages from its own cursor until more is false, waits for the selected session's attach before resyncing, and rereads the session list when the watch stream lagged. Prompts still in flight keep their optimistic rows.
• Switching sessions: selecting a session resets all of the previous session's client state (queue, summary, permission, pending prompt rows and message mapping) through one resetSessionState helper.

The bundled agent-pane/index.html is rebuilt.

Verification

• bun test src/agent-session/acpmux/ in webviews/:
  • At 16c261e (the tests only): 24 pass, 7 fail. The 7 new client tests fail, as intended.
  • At head: 38 pass, 0 fail.
  • At 154cdbb, after a review against the acpmux daemon's sources found that lag recovery read a sessionId the daemon never sends, the fixtures switched to the real shapes and 6 tests failed. 4d6b7f5 fixes them. A second review found that lag paging skipped ranges when live events landed mid-resync; 2c57221 (2 red tests) and 276e7e8 fix that.
• bun run test (268 pass), typecheck and lint:ci pass.
• build-agent-pane-web.sh --check and build-webviews-app.sh --check pass.
• The changes are TypeScript only. No in-app dogfood against a live acpmux daemon yet.

Changelog

none

🤖 Generated with Claude Code

https://claude.ai/code/session_01RYQHfug1ZVQDp4eWgwVUtD

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Summary by cubic

Keeps the cmux-next agent pane's session picker, history paging, and lag recovery in sync with the daemon, porting four client-side fixes from #16203 into AcpmuxDirectClient and matching the daemon's actual wire shapes.

Behavior changes

• The session picker refreshes on every session-list change, and a lagged watch stream rereads the list.
• Older history pages through _acpmux/events instead of reattaching, preserving the live summary, queue, and pending permission; a page landing after a selection change is discarded, and paging stops when more is false.
• Requests on a socket that isn't open reject immediately instead of hanging.
• _acpmux/lagged follows the daemon's shapes ({sessionIds, watch, dropped} or {dropped} only): it resyncs the selected session, merges missed events, and keeps in-flight prompts' optimistic rows.
• Lag recovery pages from its own cursor instead of the shared lastSeq, so a live event landing mid-resync no longer makes the next page skip the rest of the gap, and it ignores a lag notice until the selected session's attach reply has landed.
• Switching sessions resets all of the previous session's state via one resetSessionState helper.
• Adds client tests over a scripted socket and rebuilds the bundled agent-pane/index.html.

The branch is merged up to date with feat-cmux-next; the only change from that merge is the rebuilt bundle.

^{Written for commit 89fb8df. Summary will update on new commits.}

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[teamleaderleo]

Subagent review at 7eed115: REQUEST_CHANGES. _acpmux/lagged never carries sessionId (the daemon sends {sessionIds, watch, dropped} or {dropped}), so lag recovery never ran, and history read hasMore instead of more. Fixed in 154cdbb (red tests with the real shapes) and 4d6b7f5, which also pages lag recovery on more and refreshes the picker after a watch lag. A fresh review of the new head follows.

[teamleaderleo]

Subagent review at 4d6b7f5: REQUEST_CHANGES. The lag-resync loop paged from this.lastSeq, which live events advance between pages, so a gap longer than one page lost the rest. A lag notice during a select's attach also resynced from seq 0. Fixed in 2c57221 (red tests) and 276e7e8, which uses a page-local cursor and waits for attach. Still open, as non-blocking notes tracked in #16424:

• after a watch lag that dropped a purge of the selected session, the pane doesn't reselect;
• against a pre-agent-gui daemon, loadOlder can leave a gap because that daemon ignores beforeSeq.

[teamleaderleo]

Subagent review at 276e7e8: APPROVE.

• Cursor: the page-local cursor matches how the agent-gui daemon orders lag notices: it drops events after a lag until its queue drains, so the notice precedes every event after the gap.
• Attach gate: attachedGeneration never suppresses resync permanently on the connect, reconnect, missing-session, purge or attach-failure paths.
• Dedup and termination: mergeEventRecords dedupes live and paged events, and the loop stops on more: false or an empty page.
• Red then green: the 2 new tests fail against 4d6b7f5's direct.ts and pass at head.

Non-blocking, added to #16424:

• the reconnect re-attach (limit: 400) can leave a gap after a long disconnect (this predates the PR);
• the status can stay at "resyncing" if the fetch fails;
• the missing-session reconnect path pages full history.

[cubic-dev-ai]

2 issues found and verified against the latest diff

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="webviews/src/agent-session/acpmux/direct.ts">

<violation number="1" location="webviews/src/agent-session/acpmux/direct.ts:249">
P1: Lag recovery can erase a live permission prompt when the prompt exists only in the `_acpmux/permission_pending` notification: `rebuild()` clears `pendingPermission`, and this path does not preserve it as `loadOlder()` does. Preserve or reconcile the current permission while replaying missed events.</violation>

<violation number="2" location="webviews/src/agent-session/acpmux/direct.ts:259">
P2: A watch lag that dropped the selected session’s purge leaves that deleted session selected after this refresh. Reconcile a missing `selectedSessionId` using the same fallback/reset/attach behavior as the purge handler.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P1: Lag recovery can erase a live permission prompt when the prompt exists only in the _acpmux/permission_pending notification: rebuild() clears pendingPermission, and this path does not preserve it as loadOlder() does. Preserve or reconcile the current permission while replaying missed events.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At webviews/src/agent-session/acpmux/direct.ts, line 245:

<comment>Lag recovery can erase a live permission prompt when the prompt exists only in the `_acpmux/permission_pending` notification: `rebuild()` clears `pendingPermission`, and this path does not preserve it as `loadOlder()` does. Preserve or reconcile the current permission while replaying missed events.</comment>

<file context>
@@ -213,21 +220,53 @@ export class AcpmuxDirectClient {
+      if (generation !== this.selectionGeneration || this.selectedSessionId !== sessionId) return;
+      const missed: EventRecord[] = result?.events ?? [];
+      this.events = mergeEventRecords(this.events, missed);
+      this.rebuild();
+      if (result?.more !== true || missed.length === 0) break;
+    }
</file context>

[cubic-dev-ai]

P2: A watch lag that dropped the selected session’s purge leaves that deleted session selected after this refresh. Reconcile a missing selectedSessionId using the same fallback/reset/attach behavior as the purge handler.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At webviews/src/agent-session/acpmux/direct.ts, line 254:

<comment>A watch lag that dropped the selected session’s purge leaves that deleted session selected after this refresh. Reconcile a missing `selectedSessionId` using the same fallback/reset/attach behavior as the purge handler.</comment>

<file context>
@@ -213,21 +220,53 @@ export class AcpmuxDirectClient {
+  /// session_changed notices dropped by a watch lag: reread the whole list.
+  private async refreshSessions(): Promise<void> {
+    const watched = await this.request("_acpmux/watch", { enabled: true });
+    this.sessions = (watched?.sessions ?? []).filter((session: Session) => session.sessionId);
+    this.emit("session changed");
   }
</file context>

[teamleaderleo]

89fb8df merges feat-cmux-next (#16425) into the reviewed head 276e7e8. The only conflict was the generated agent-pane/index.html, rebuilt from the merged sources; build-agent-pane-web.sh --check passes. After the merge, webviews bun run test (269 pass), typecheck, lint:ci and build-webviews-app.sh --check pass. There are no hand edits beyond the reviewed commits.

[teamleaderleo]

Merging with only cmux-next swift test outstanding. That's the lane's existing debt, owned by cx-next-swift-tests (same as #16206, #16231 and #16425), and this PR changes only TypeScript and the generated bundle. Every other check is green, and a fresh review approved 276e7e8; 89fb8df only merges the base in and regenerates the bundle.